Printed circuit board edge card connector having two non-redundant rows of contacts

ABSTRACT

A SIMM connector is provided with two rows of contacts, wherein the contacts are offset in the direction of the row of contacts with respect to each other such that the adjacent contact pads of the SIMM card are contacted alternately on opposite sides of the board. Elimination of redundant contact points enables the contacts to be stamped from the plane of sheet metal into relatively wide beams that enable sufficient contact force but large elastic range, and in particular enable a whole row of contacts to be inserted into the housing in one manufacturing step to reduce manufacturing costs.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a connector for mating with a printed circuitboard edge card.

2. Summary of the Prior Art

In applications such as SIMM (Single In-Line Memory Module) and DIMM(Dual In-Line Memory Module) cards for computer systems, memory chipsare positioned on a printed circuit and interconnected by circuit tracesthereon to a plurality of juxtaposed circuit pads arranged along theedge of the card which can then be plugged into a connector forinterconnecting the memory modules to a computer. In many applications,the card must be unpluggable in order to exchange or replace the card.The contact pads arranged along the edge of the card are usuallyprovided on either side of the card. In SIMM cards, aligned contact padson opposite sides of the board are electrically interconnected. Thecomplementary edge card connector typically has contacts for contactingthe contact pads on both sides of the board. An example is shown in U.S.Pat. No. 4,575,172, where each contact has a pair of contact points forcontacting opposed aligned contact pads of the PCB. One of the contactpoints is thus redundant.

The contact pads of most SIMM cards are of tin or similar materials thatmay oxidize, the complementary contacts of the mating connector alsobeing of a similar material. Due to the presence of oxidation layersthat may impair electrical conductivity at the contact surfacesrelatively high contact forces are required, and if possible a certainamount of rub during plugging connection in order to break through theoxide layers is desired. High contact forces and large numbers ofcontacts eliminates the practicability of having a simple pluggingconnection, which has led to the design of low insertion force systemssuch as the pivoting board solution as shown in U.S. Pat. No. 4,575,172.The pivoting lever arm effect enables high contact forces for a largenumber of contacts to be provided. In tin connection surfaces, forexample typically used for SIMM card connectors, the requirement forhigh contact forces in tight spacing means that the contacts arerelatively rigid and have a small elastic range. Redundant contacts areimportant in view of this, because warping or thickness tolerances of amating PCB may be excessive for a single contact.

In order to generate high forces in tight spacing, SIMM connectors oftenhave contacts edge stamped from sheet metal, where the contact springbeams flex in the plane of the sheet metal. Such contacts are usuallyindividually assembled to connector housings by stitching, whichrequires a relatively high manufacturing cycle time. There are manyother types of low or zero insertion force connection systems, forexample some of them hold the opposed contact points apart to enableinsertion of the edge card therebetween, subsequently enabling biasingtogether of the contacts against the contact pads by actuation of acamming mechanism or similar means. Such cammed low insertion or zeroinsertion force systems are often used with gold plated contact surfacesbecause much less contact pressure, and no rubbing effect is requiredbetween gold contact surfaces. Due to the lower contact force, edge cardconnector systems with gold plated surfaces are sometimes simply pluggedwithout reducing the insertion forces because the contact forces aresufficiently low to enable this. In a given space, elastic range(flexibility) can also be increased due to the lesser requirement forcontact force. Gold plating however, increases the cost of theconnection system.

It would be desirable to reduce the cost of such connection systemswhilst nevertheless maintaining the requisite level of reliability andperformance.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a SIMM connectorthat is cost-effective, but nevertheless reliable, and enabling lowinsertion forces.

It is a further object of this invention to provide a cost effective andreliable edge card connector that can support bending of a board forconnection thereto whilst nevertheless ensuring reliable contact.

Objects of this invention have been achieved by providing an edge cardconnector comprising an insulative housing and a plurality of resilientcontacts mounted therein and disposed in two rows separated by a gap forreceiving an edge card therein, a first row having a plurality ofjuxtaposed contacts, and a second row having a plurality of juxtaposedcontacts that are offset with respect to the first row such thatcontacts of first and second rows are for connection to contact padsthat are offset in the direction of the rows with respect to each other.Advantageously therefore, redundant contacts are eliminated therebyenabling each row to have less (for example half) the number of contactscompared to prior art SIMM connectors. Either a more compact spacingbetween the edge card contact pads is enabled, or larger contacts can beprovided in the connector in order to produce a greater contact force,for example for tin plated contacts.

In an advantageous embodiment, contact points of the opposed contactscan be at different heights, whereby the contact with the lower contactpoint (i.e. closer to the base of the connector) may be provided with anacute angle V-shaped bend in order to elongate the spring path, therebyincreasing the elastic deflection of the contact beam. Adjustment tolarge tolerances in bending of the board for connection thereto is thusenabled in a reliable manner. The contacts can also be mounted in thehousing in a pre-stressed manner by abutment of an extension at the freeend of the contacts with a shoulder of the housing such that accuratepositioning of the contact surfaces is ensured, and if desired greatercontact forces can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantageous features will be apparent from the description,drawings and claims.

An embodiment of this invention will now be described, by way ofexample, with reference to the figures, whereby;

FIG. 1 is a cross sectional view through a SIMM connector according tothis invention;

FIG. 2 is an isometric view of the SIMM card of FIG. 1;

FIG. 3 is a top view of the mating face of part of a SIMM connectoraccording to this invention;

FIG. 4 is an isometric view of the bottom mounting face of part of theSIMM connector;

FIG. 5 is an isometric view of a short contact;

FIG. 6 is an isometric view of the contact stamped and formed from sheetmetal still attached to a carrier strip;

FIG. 7 is an isometric view of a long contact.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a SIMM connector 2 is shown comprising aninsulative housing 4, and contacts 6. There 15 is a first row 8 of longcontacts 10 and a second row 12 of short contacts 14 parallel thereto.

The insulative housing 4 comprises a plurality of terminal receivingcavities 16 and 18 for receiving the contacts 10 and 14 respectively.The connector housing extends from a mounting face 20 to a cardreceiving face 22. An edge of a printed circuit board 24 is insertablefrom the card receiving face 22 between the contact rows 8 and 12inclined at a certain angle (20-30°) without requiring any insertionforce. The card 24 can then be pivoted to the vertical position therebyabutting and resiliently outwardly biasing the opposed contacts 10 and14 for contact against contact pads 26,28 respectively.

Referring to FIG. 7, the long contact 10 is stamped and formed fromsheet metal and comprises a connection section 34 contacting a printedcircuit board, a base section 32, and a contact section 34 extendingfrom the base section and comprising a contact protrusion 36 proximate afree end 38. The base section 32 is substantially planar and has a widthW larger than the free end 38. Between the contact section 34 and thebase section 32, is a spring section 33. The spring section has agradually decreasing width from the base section 32 to the contactsection 36. The wide base section 32 enables the contact to be securelyseated in slots 40 (see FIG. 4) extending into opposed side walls 42 ofthe contact receiving cavity 16. Although not shown in FIG. 7, lateraledges 44 of the base section can be provided with retention barbs. Thecontact can be stitched into the slots 40 from the printed circuit boardmounted face 20 of the housing 4.

During manufacturing, the contacts 10 of the row 8 can be stamped andformed in the same pitch as the positioning within the housing, similarto what is shown in FIG. 6 for the short contacts 14, whereby the wholerow 8 of contacts 10 can be inserted into the housing in a singleinsertion movement by an assembly machine which grips the contacts andcuts away the inter-linking metal parts of the carrier strip 41 prior toinsertion in the housing. This reduces assembly costs in comparison tostitching the contacts or mounting the contacts individually into theirrespective cavities, because it reduces the manufacturing cycle time.

The large width of the base portion 32 enables very stabile and strongsupport of the contact within the housing, whilst nevertheless enablingprovision of optimal resiliency and flexibility via the tapering of thespring arm 33 from the base 32 to the contact protrusion 36. The largewidth W of the base portion 32 is possible because contacts 14 of thesecond row 12 are offset by a distance d (see FIG. 4) that is equivalentto the pitch of the contact pads 26,28 of the PCB 24.

In SIMM connectors, contact pads 28 or 26 are inter-connected to acontact pad, aligned therewith on the respective opposite side of thecircuit board. By contacting alternate contact pads 26 on one side 23 ofthe PCB 24, by the connector contact 8, and also contacting alternatecontact pads 28 offset therefrom by distance D on the other side 25 ofthe PCB 24, all the connector contacts of the printed circuit board edgeare contacted (without redundancy). Rather than producing redundantcontacts as in the prior art, therefore, individual contacts 10,14 areprovided with higher flexibility in order to compensate for eventualwarping of the printed circuit board 24. The use of less contacts alsoenables the base section to be broader and the spring section togenerate sufficiently high forces for oxidizing (tin) contact surfaces.An important advantage is the orientation of the contacts formed formthe plane of the sheet metal, and inserted in the cavities in thisorientation, to enable simultaneous assembly of the contacts into thehousing.

Referring to FIG. 5, the short contact 14 comprises a connection section30, a base section 32' a spring section 33', and a contact section 34'proximate a free end 38'. Due to the lower position of the contactprotrusion 36' within the connector as shown in FIG. 1 with respect tothe long contact 10, there is less height available for the springsection 33'. In order to provide the contact with a large elastic range,the spring section 33' is provided at an oblique angle andinterconnected to the base section 32' via a V-shaped bend 50 having anacute angle a (see FIG. 1). The effective spring length of the springsection 33' is thus enhanced in a compact manner, whilst neverthelessproviding the requisite spring force. The spring section 33' also tapersfrom the wide base section 32' to the narrow contact protrusion 36' in asimilar manner to the long contact 10.

As shown in FIG. 6 and already explained hereabove for the long contact10, the contacts 14 can be stamped and formed from sheet metal at apitch ready for insertion of the whole row of contacts in one assemblyoperation into the cavities 18 of the housing.

As shown in FIG. 1, the free ends 38,38' of the contacts abut shoulders52,52' respectively of the housing to locate the contact protrusions36,36' precisely. The shoulders 52,52' are provided by provision ofcut-outs 54,54' that enable visual inspection from the cord receivingside of correct assembly and positioning of the contacts 10,14 withinthe housing. Such visual inspection can be provided along themanufacturing process by means of video cameras, for example, formingpart of the quality control procedures. If desired, the contracts canalso be prestressed in order to increase the contact forces.

We claim:
 1. An edge card connector for connection to juxtaposed contactpads disposed on either side and along an edge of a PCB, the connectorcomprising an insulative housing extending from a mounting face to acard receiving face, a first row of juxtaposed long contacts and asecond non-redundant row of juxtaposed short contacts parallel to thefirst row and spaced therefrom for receiving the PCB therebetween, eachlong contact having a contact protrusion at a certain height from themounting face and each short contact having a contact protrusion at aheight less than the contact protrusion of the long contact such thatthe connector is adapted for low insertion force entry of the PCBbetween the contact rows at an oblique angle, the PCB subsequentlypivotable to engage resiliently the contact protrusions against the PCBcontact pads, wherein the contacts of the first row are offset apredetermined distance in the direction of the rows, with respect to thecontacts of the second row.
 2. The connector of claim 1 wherein theoffset distance is equal to half the distance between adjacent contactsof one of the rows.
 3. The connector of claim 1 wherein the shortcontact comprises a base section, a spring section, and a contactsection comprising the contact protrusion, the spring section being inthe shape of a beam extending between the base section and contactsection and having a "V" shaped bend.
 4. The connector of claim 3wherein the bend has an acute angle.
 5. The connector of claim 1 whereinthe contacts have substantially planar base sections for secure mountingand retention in slots of the housing, the base sections and slotssubstantially disposed in a plane parallel to the contact row direction.6. The connector of claim 5 wherein the contacts have spring sectionsthat extend from the base sections and taper to the contact protrusion.7. The connector of claim 1 wherein the contacts have free ends thatproject into cavities that form shoulders against which the free endsabut, for positioning the contact protrusions, and whereby the free endsare visible from the card receiving end of the connector through thecavities, for visual inspection thereof.
 8. The connector of claim 1wherein each row of contacts is stamped and formed from a plane of sheetmetal at a contact pitch corresponding to the contact pitch in theassembled connector, such that a whole row of contacts can be insertedand locked into the connector housing in one assembly insertion step.